 /*
  * $Header: /cvshome/build/org.osgi.framework/src/org/osgi/framework/ServiceReference.java,v 1.20 2007/02/21 16:49:05 hargrave Exp $
  *
  * Copyright (c) OSGi Alliance (2000, 2007). All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package org.osgi.framework;

 /**
  * A reference to a service.
  *
  * <p>
  * The Framework returns <code>ServiceReference</code> objects from the
  * <code>BundleContext.getServiceReference</code> and
  * <code>BundleContext.getServiceReferences</code> methods.
  * <p>
  * A <code>ServiceReference</code> object may be shared between bundles and
  * can be used to examine the properties of the service and to get the service
  * object.
  * <p>
  * Every service registered in the Framework has a unique
  * <code>ServiceRegistration</code> object and may have multiple, distinct
  * <code>ServiceReference</code> objects referring to it.
  * <code>ServiceReference</code> objects associated with a
  * <code>ServiceRegistration</code> object have the same <code>hashCode</code>
  * and are considered equal (more specifically, their <code>equals()</code>
  * method will return <code>true</code> when compared).
  * <p>
  * If the same service object is registered multiple times,
  * <code>ServiceReference</code> objects associated with different
  * <code>ServiceRegistration</code> objects are not equal.
  *
  * @see BundleContext#getServiceReference
  * @see BundleContext#getServiceReferences
  * @see BundleContext#getService
  * @ThreadSafe
  * @version $Revision: 1.20 $
  */

 public interface ServiceReference extends Comparable {
     /**
      * Returns the property value to which the specified property key is mapped
      * in the properties <code>Dictionary</code> object of the service
      * referenced by this <code>ServiceReference</code> object.
      *
      * <p>
      * Property keys are case-insensitive.
      *
      * <p>
      * This method must continue to return property values after the service has
      * been unregistered. This is so references to unregistered services (for
      * example, <code>ServiceReference</code> objects stored in the log) can
      * still be interrogated.
      *
      * @param key The property key.
      * @return The property value to which the key is mapped; <code>null</code>
      * if there is no property named after the key.
      */
     public Object getProperty(String key);

     /**
      * Returns an array of the keys in the properties <code>Dictionary</code>
      * object of the service referenced by this <code>ServiceReference</code>
      * object.
      *
      * <p>
      * This method will continue to return the keys after the service has been
      * unregistered. This is so references to unregistered services (for
      * example, <code>ServiceReference</code> objects stored in the log) can
      * still be interrogated.
      *
      * <p>
      * This method is <i>case-preserving </i>; this means that every key in the
      * returned array must have the same case as the corresponding key in the
      * properties <code>Dictionary</code> that was passed to the
      * {@link BundleContext#registerService(String[],Object,java.util.Dictionary)}
      * or {@link ServiceRegistration#setProperties} methods.
      *
      * @return An array of property keys.
      */
     public String [] getPropertyKeys();

     /**
      * Returns the bundle that registered the service referenced by this
      * <code>ServiceReference</code> object.
      *
      * <p>
      * This method must return <code>null</code> when the service has been
      * unregistered. This can be used to determine if the service has been
      * unregistered.
      *
      * @return The bundle that registered the service referenced by this
      * <code>ServiceReference</code> object; <code>null</code> if
      * that service has already been unregistered.
      * @see BundleContext#registerService(String[],Object,java.util.Dictionary)
      */
     public Bundle getBundle();

     /**
      * Returns the bundles that are using the service referenced by this
      * <code>ServiceReference</code> object. Specifically, this method returns
      * the bundles whose usage count for that service is greater than zero.
      *
      * @return An array of bundles whose usage count for the service referenced
      * by this <code>ServiceReference</code> object is greater than
      * zero; <code>null</code> if no bundles are currently using that
      * service.
      *
      * @since 1.1
      */
     public Bundle[] getUsingBundles();

     /**
      * Tests if the bundle that registered the service referenced by this
      * <code>ServiceReference</code> and the specified bundle use the same
      * source for the package of the specified class name.
      * <p>
      * This method performs the following checks:
      * <ol>
      * <li>Get the package name from the specified class name.</li>
      * <li>For the bundle that registered the service referenced by this
      * <code>ServiceReference</code> (registrant bundle); find the source for
      * the package. If no source is found then return <code>true</code> if the
      * registrant bundle is equal to the specified bundle; otherwise return
      * <code>false</code>.</li>
      * <li>If the package source of the registrant bundle is equal to the
      * package source of the specified bundle then return <code>true</code>;
      * otherwise return <code>false</code>.</li>
      * </ol>
      *
      * @param bundle The <code>Bundle</code> object to check.
      * @param className The class name to check.
      * @return <code>true</code> if the bundle which registered the service
      * referenced by this <code>ServiceReference</code> and the
      * specified bundle use the same source for the package of the
      * specified class name. Otherwise <code>false</code> is returned.
      *
      * @since 1.3
      */
     public boolean isAssignableTo(Bundle bundle, String className);

     /**
      * Compares this <code>ServiceReference</code> with the specified
      * <code>ServiceReference</code> for order.
      *
      * <p>
      * If this <code>ServiceReference</code> and the specified
      * <code>ServiceReference</code> have the same
      * {@link Constants#SERVICE_ID service id} they are equal. This
      * <code>ServiceReference</code> is less than the specified
      * <code>ServiceReference</code> if it has a lower
      * {@link Constants#SERVICE_RANKING service ranking} and greater if it has a
      * higher service ranking. Otherwise, if this <code>ServiceReference</code>
      * and the specified <code>ServiceReference</code> have the same
      * {@link Constants#SERVICE_RANKING service ranking}, this
      * <code>ServiceReference</code> is less than the specified
      * <code>ServiceReference</code> if it has a higher
      * {@link Constants#SERVICE_ID service id} and greater if it has a lower
      * service id.
      *
      * @param reference The <code>ServiceReference</code> to be compared.
      * @return Returns a negative integer, zero, or a positive integer if this
      * <code>ServiceReference</code> is less than, equal to, or
      * greater than the specified <code>ServiceReference</code>.
      * @since 1.4
      */
     public int compareTo(Object reference);
 }

